1. Field of the Invention
The present invention relates to a liquid ejecting apparatus and a liquid ejecting method in which liquid drops are ejected through an ejecting hole/holes formed in a liquid ejecting head onto an object to be processed.
2. Description of the Related Art
An ink-jet recording apparatus provided with an ink-jet recording head for image recording is a representative liquid ejecting apparatus. Other liquid ejecting apparatuses include an apparatus provided with a dye-ejecting head for manufacturing color filters for, for example, liquid crystal displays, an apparatus provided with an ejecting head for ejecting an electrode forming material (conductive paste) ejecting head for forming electrodes of organic EL displays and face emission displays (FEDs), an apparatus provided with a an ejecting head for ejecting a bioorganic substance to manufacture biochips and an apparatus provided with a sample-ejecting head serving as a precision pipette.
The ink-jet recording apparatus, namely, a representative liquid ejecting apparatus, generates comparatively low noise during a printing operation and is capable of forming small dots in a high dot density. Thus the ink-jet recording apparatus is used for various printing operations including a color-picture printing operations these days.
Generally, the ink-jet recording apparatus includes an ink-jet recording head mounted on a carriage capable reciprocating in directions along the width of a recording medium (an object to be processed), such as a recording paper sheet, namely, in a scanning direction and a direction opposite the scanning direction, a feed mechanism for feeding the recording medium in a direction perpendicular to the scanning direction, namely, a feed direction, and a platen supporting the recording medium that is fed by the feed mechanism to position the recording medium relative to the recording head.
In this ink-jet recording apparatus, the recording head is controlled according to printing data to jet ink drops onto the recording medium for printing. When the recording head mounted on the carriage is capable of jetting drops of, for example, black, yellow, cyan and magenta inks, the ink-jet recording apparatus is able to achieve full-color printing by using those color inks in proper discharge ratios as well as text printing using only the black ink.
There is an ink-jet recording apparatus of a type capable of selectively operating in either a borderless printing mode for printing the entire surface of a recording medium without leaving any margins or a bordered printing mode for printing part of the surface of a recording medium so as to leave unprinted margins on the peripheral portion of the recording medium.
When the ink-jet recording apparatus operates in a borderless printing mode, the ink-jet recording apparatus prints an area of a size larger than that of the recording medium to compensate for the positional displacement of the recording medium and the carriage.
Namely, when it is desired to print the recording medium without leaving any margins along the side edges, i.e., the edges extending in the feed direction, of the recording medium, the ink-jet recording apparatus is capable of setting the opposite ends of a scanning range in which the recording head moves for printing at positions outside the side edges of the recording medium to jet ink drops on areas outside the side edges of the recording medium.
Further, when it is desired to print the recording medium without leaving any margins along the leading and the trailing edges, i.e., the edges extending in the scanning direction, the ink-jet recording apparatus specifies a printing area extending beyond the leading edge of the recording medium and behind the trailing edge of the recording medium.
Ink drops jetted onto areas outside the recording medium are absorbed by an absorber, such as sponge, placed in a space behind the recording medium opposite to the recording head.
As mentioned above, ink drops are jetted on areas outside the leading and trailing edges and/or the side edges of the recording medium when it is desired to print the entire surface of the recording medium without leaving any margins along the edges of the recording medium. Consequently, ink mist flowed into a space behind the recording medium adheres to edge parts of the back surface of the recording medium to stain the recording medium with the ink. Such staining is a serious problem particularly when a recording medium is printed on both sides, or when printing a recording medium of which both sides are to be used, such as a postcard.
Moreover, the ink mist soils the interior of the ink-jet recording apparatus, sticks to the electric circuit and the linear scale to cause the electric circuit and the linear scale to malfunction, and deposits on the ink cartridge to dirty the user's hand.
Generally, a feed mechanism for feeding the recording medium is provided with feed rollers disposed opposite to each other to nip and feed the recording medium. One of the feed rollers opposite to each other is a drive roller formed by coating the circumference of a metal roller with an alumina coating formed by baking and having a frictional circumference and the other is a driven roller of a plastic material.
Generally, the recording medium fed into a recording zone is charged due to rubbing by the feed rollers when the recording medium is brought into contact with and is separated from the feed rollers, rubbing by the following recording medium when recording mediums are fed by an automatic sheet feeder or frictional contact of the recording medium with structural members on a feed passage. The charged recording medium tends to attract the ink mist to its back surface.
A method of solving such a problem employs a static eliminating means, such as a static elimination brush, to eliminate static charges from the charged recording medium. The static eliminating means is disposed necessarily at a position downstream the feed mechanism including the pair of feed rollers with respect to the feed direction and hence the printing zone is spaced a long distance apart from the feed mechanism. Consequently, the accuracy of feeding the recording medium is liable to be deteriorated and the recording medium tends to float unstably. The static elimination brush rubs the recording medium, such as a paper sheet, and produces paper powder. The thus produced paper powder adheres to the ejecting holes of the recording head and deteriorates the ink drop jetting ability of the recording head.
The size of ink drops to be jetted by the recording head is required to be reduced to meet the recent demand for higher print quality. Since the velocity of small ink drops decreases rapidly due to the viscous resistance of air, it is possible that ink drops jetted by the recording head toward areas outside the recording medium during an operation in the borderless printing mode are unable to reach the absorber so that ink mist is generated. The ink mist flowed into a space behind the recording medium adheres to edges parts of the back surface of the recording medium to stain the recording medium with the ink. Such staining is a serious problem particularly when the recording medium is printed on both sides, or when printing a recording medium of which both sides are to be printed, such as a postcard.
The necessity of an ink mist preventing means is great in order to prevent the conversion of ink drops jetted onto areas outside the recording medium into ink mist during an operation in the borderless printing mode. However, the operation in the bordered printing mode does not necessarily need the ink mist preventing means and it is possible that the ink mist preventing means employed for the operation in the borderless printing mode exerts a bad influence on the operation in the bordered printing mode.
In some cases, an ink drop jetted in some jetting mode fissions into a large main particle and a small satellite particle of a weight far smaller than that of the main particle. Even if the ink-jet recording apparatus is provided with a mist preventing means for preventing mist formation, the mist preventing means may be effective in preventing the large main particle from floating in a mist, but may be ineffective in preventing the small satellite particle of a weight far smaller than that of the main particle from floating in a mist.
Even in a state where an ink drop jetted toward a printing area in a recording medium can fission into a large main particle and a small satellite particle, the large main particle is able to reach the recording medium, while it is possible for the small satellite particle not to reach the recording medium and the small satellite particle forms a mist. Particularly, when a drop of a pigment ink fissions into a large main particle and a small satellite particle, there is a tendency that the small satellite particle is unable to reach the recording medium and form a mist.
The ink mist soils the interior of the ink-jet recording apparatus, sticks to the electric circuit and the linear scale to cause the electric circuit and the linear scale to malfunction, and deposits on the ink cartridge to dirty the user's hand.
Even if a small ink drop reaches the recording medium without forming a mist, the small ink drop is unable to fly stably and unable to impact on the recording medium at a desired position because the velocity of the small ink drop decreases rapidly. Consequently, it is possible that a blurred or rough picture is formed in a low print quality.
It may be possible to make sure that a small ink drop impacts on a recording medium at a desired position by jetting the small ink drop at a high initial velocity. However, the small ink drop is stretched and is caused to fission into a main particle and a satellite particle if the initial velocity of the ink drop is excessively high. If the ink-jet recording apparatus operates in an operating mode in which a satellite particle is liable to be produced, the main particle and the satellite particle fall at different positions, respectively, with respect to the scanning direction. Consequently, a laterally elongate dot is formed on the recording medium, and the laterally elongate dot reduces the sharpness in a printed image and deteriorates print quality. A problem causing change of color tone arises due to the union or separation of the main particle and the satellite particle resulting from differences in individual property, thermal environment and/or platen gap.
When an ink drop fissions into a main particle and a satellite particle, there is a tendency that the velocity of the main particle increases according to the increase of the initial velocity, whereas the velocity of the satellite particle does not increase according to the increase of the initial velocity. Thus the difference between the respective velocities of the main particle and the satellite particle increases and the distance between positions where the main particle and the satellite particle hit the recording medium, respectively, increases with the increase of the initial velocity, aggravating the problem relating to the deterioration of print quality and the change of color tone.
When the ink-jet recording apparatus is provided with some mist preventing means, the mist preventing means must continue to be effective from the start and the end of the printing operation.